Biopolar electrosurgical instruments apply radiofrequency (RF) energy to a surgical site to cut, ablate, or coagulate tissue. A particular application of these electrosurgical effects is to seal blood vessels or tissue sheets. A typical instrument takes the form of a pair of opposing jaws or forceps, with one or more electrodes on each jaw tip. In an electrosurgical procedure, the electrodes are placed in close proximity to each other as the jaws are closed on a target site such that the path of alternating current between the two electrodes passes through tissue within the target site. The mechanical force exerted by the jaws and the electrical current combine to create the desired surgical effect. By controlling the level of mechanical and electrical parameters, such as the pressure applied by the jaws, the gap distance between electrodes, and the voltage, current, frequency, and duration of the electrosurgical energy applied to the tissue, the surgeon can coagulate, cauterize, or seal tissue toward a therapeutic end.
Electrosurgical procedures can be performed in an open environment, through conventional incisions, or using laparoscopic procedures. In laparoscopic procedures, the electrosurgical instrument must be able to fit through a cannula or trocar having a very small inner diameter that is typically between 5 mm and 10 mm. It is possible to make an electrosurgical instrument small enough to meet this size requirement. Nevertheless, the push to make instruments smaller often competes against other equally important design criteria.
The compression force exerted by the instrument is one of the most important design criteria that competes with instrument size. Ordinarily, a high compression force between the jaws is needed to form a proper seal within a reasonably short amount of time. Without sufficient compression force, the instrument may not be able to form a proper seal, or may form a proper seal only after a long time. It can be very difficult to create sufficient compression force with a smaller electrosurgical instrument because as the size of the instrument decreases, the percentage of space taken up by non-structural elements in the jaws increases. For example, the components that control tissue cutting, jaw actuation, articulation and power delivery all take up space in the jaws. Each component requires the removal of material from the jaws to provide space for the component. This reduces material mass and stiffness in the jaws, thereby reducing the compression force that can be created.
Based on the foregoing, there is a need for improved electrosurgical devices that can be reduced in size without sacrificing important parameters like compressive strength.